Learn Hardcore Finnish: Harjoittelen sanastoa kirjoittamalla lyhyitä tarinoita muistikirjaani. - I practice vocabulary by writing short stories in my notebook.

The verb harjoitella (“to practice”) almost always takes its object in the partitive when you’re practicing a skill, subject, or material in an ongoing, incomplete way.

harjoittelen sanastoa ≈ “I practice vocabulary / I’m working on vocabulary” (ongoing, not “all of it”)
The partitive sanastoa suggests an indefinite amount of vocabulary, not a clearly bounded whole.

If you said:

harjoittelen sanaston – this would be unusual and would suggest a very specific, complete set of vocabulary that you’re going to go through entirely, which is not how people normally say it.

So sanastoa is the natural choice because it fits the idea of practicing some vocabulary in general, not finishing a fixed list.

Could you say harjoittelen sanaston at all, or is it wrong?

It’s not strictly “wrong”, but it is very uncommon and feels odd.

harjoittelen sanaston would imply “I will practice the whole set of vocabulary (that we both know about)”, as if you had a clearly defined list and your aim is to cover it completely.
In real usage, Finns almost always say harjoittelen sanastoa for “I practice vocabulary”.

So, grammatically possible but stylistically unnatural in most situations.

What exactly is kirjoittamalla? Is it a verb form, and how is it formed?

Kirjoittamalla is the 3rd infinitive in the adessive case, often called the “-malla/-mällä form”. It expresses means or manner and usually translates as “by doing X”.

Formation:

Take the verb stem: kirjoittaa → stem kirjoitta-
Add -ma/-mä: kirjoittama-
Add the adessive ending -lla/-llä: kirjoittamalla

Meaning:

kirjoittamalla = “by writing”

So kirjoittamalla lyhyitä tarinoita means “by writing short stories”.

Why do we use kirjoittamalla instead of something like kirjoittamalla lyhyitä tarinoita → kirjoitan lyhyitä tarinoita?

Both are grammatical, but they express different structures:

Harjoittelen sanastoa kirjoittamalla lyhyitä tarinoita.
= “I practice vocabulary by writing short stories.”
Here kirjoittamalla expresses method/means.
Harjoittelen sanastoa ja kirjoitan lyhyitä tarinoita.
= “I practice vocabulary and write short stories.”
Now you just have two actions side by side; the connection of “means” is weaker.

The -malla form explicitly answers “How? By doing what?”
So kirjoittamalla is used to highlight that writing is the method of practicing.

Why are lyhyitä tarinoita in the partitive plural, instead of lyhyet tarinat?

Lyhyitä tarinoita is partitive plural:

lyhyt → lyhyitä (partitive plural)
tarina → tarinoita (partitive plural)

Reasons:

It expresses an indefinite amount: “some short stories”, not a specific, counted set.
The action is ongoing/habitual: you’re not talking about a fixed batch of stories that you complete once, but your general method.

If you said:

kirjoittamalla lyhyet tarinat – that would sound like there is a known, limited set of “the short stories” which you then write (all of them). That’s usually not what is meant here.

So lyhyitä tarinoita matches the idea of practicing by writing some short stories (indefinite, repeated).

Why do lyhyitä and tarinoita both change form? Why not just lyhyitä tarinat?

In Finnish, adjectives agree with the noun in:

number (singular/plural)
case (nominative, partitive, etc.)

Since tarinoita is partitive plural, the adjective lyhyt must also be partitive plural → lyhyitä.

So:

nominative plural: lyhyet tarinat (“the short stories”)
partitive plural: lyhyitä tarinoita (“(some) short stories”)

A mixed form like lyhyitä tarinat is ungrammatical because the adjective and noun don’t match.

What does muistikirjaani consist of? How is that form built?

Muistikirjaani packs several things into one word:

muistikirja – “notebook”
-an (illative singular) – “into”
- base illative: muistikirjaan = “into the notebook”
-ni – 1st person singular possessive suffix = “my”

When you add -ni to illative -an, it fuses and you get:

muistikirja + an + ni → muistikirjaani

So muistikirjaani means “into my notebook” in a single word.

Does muistikirjaani mean “in my notebook” or “into my notebook”? What’s the nuance?

Muistikirjaani is in the illative case, which basically means “into”:

muistikirjaani ≈ “into my notebook”

For “in my notebook”, the most neutral form would be muistikirjassani:

muistikirja (notebook)
-ssa (inessive = “in”)
-ni (my) → muistikirjassani = “in my notebook”

In practice, with verbs like kirjoittaa, Finns often use the illative (muistikirjaani) to mean something very close to English “in my notebook”, because writing typically goes into a notebook. So the literal spatial idea “into” fits the action well.

Why isn’t there a separate word for “in” or “into” before muistikirjaani, like in English?

Finnish usually doesn’t use prepositions for basic location and direction. Instead, it uses case endings on nouns.

Examples:

muistikirjassa = “in the notebook” (inessive)
muistikirjaan = “into the notebook” (illative)
muistikirjasta = “out of the notebook” (elative)

So instead of “in my notebook”, Finnish packs everything into muistikirjassani (“notebook-in-my”), and instead of “into my notebook”, it uses muistikirjaani (“notebook-into-my”). The case ending replaces the preposition.

Could we change the word order, for example to Kirjoittamalla lyhyitä tarinoita muistikirjaani harjoittelen sanastoa?

Yes, that sentence is grammatically fine:

Kirjoittamalla lyhyitä tarinoita muistikirjaani harjoittelen sanastoa.

Finnish word order is quite flexible. The basic version:

Harjoittelen sanastoa kirjoittamalla lyhyitä tarinoita muistikirjaani.

places harjoittelen sanastoa first, so the focus is on the activity “I practice vocabulary”, and then explains how.

If you start with Kirjoittamalla…, you slightly emphasize the method (“By writing short stories in my notebook, I practice vocabulary”). Both are correct; the difference is mainly in emphasis and style, not grammar.

Is there any difference between harjoittelen sanastoa and something like opettelen sanastoa?

Yes, there’s a nuance:

harjoitella = to practice, to drill something you already more or less know, to improve fluency or recall.
opetella = to learn, study, memorize something new, usually more actively, often aiming to “get it into your head” for the first time.

So:

Harjoittelen sanastoa – you are practicing vocabulary (maybe words you’ve already studied).
Opettelen sanastoa – you are learning/memorizing vocabulary (perhaps new words).

Both are possible; the given sentence specifically emphasizes practice rather than initial learning.

Why doesn’t Finnish use articles like “a” or “the” in this sentence?

Finnish simply doesn’t have articles like “a/an” or “the”. The ideas of definiteness and indefiniteness are shown in other ways, mainly by:

context
case choice (e.g. partitive vs. total object)
word order
sometimes using demonstratives like se (“that”) if you really need to be explicit

So:

sanastoa could be “vocabulary”, “some vocabulary”
lyhyitä tarinoita could be “short stories”, “some short stories”

The language relies on context rather than articles, so you just say the bare nouns with appropriate case endings.